Determination of Thermodynamic Parameters in the Cu1.95Ni0.05S Phase-Transition Regions

X-ray diffraction and differential thermal analysis data obtained in the Cu1.95Ni0.05S phase-transition region are analyzed. It is established that the low-temperature rhombic alpha phase in Cu1.95Ni0.05S transforms to the hexagonal beta phase at temperatures of 370-390 K and to the cubic gamma phase at temperatures of 740-765 K according to the scheme . It is determined (using the temperature dependence of differential thermal analysis) that the transition alpha -> beta is accompanied by heat absorption while the transition beta -> gamma is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of similar to 10(-20) cm(3) at temperature rates of 0.11 and 0.08 K-1. It is demonstrated that the transition alpha -> gamma is accompanied by alternation of the structures passing through the intermediate beta phase, which is incommensurate with respect to the alpha and gamma phases.